Coupling of Drill String Whirl and Magnus Effect in Deepwater Drilling

Abstract

Abstract. In deepwater riserless drilling, the effects of the drillship’s motion and ocean currents on the drill string create complex dynamics that remain poorly understood. Previous studies revealed self-excited vibration caused by the friction of the heave compensator and forced vibration in the torsional direction due to heave. Thus, in deepwater drilling, new phenomena are likely to emerge in the drill string’s dynamic behavior. This study focused on the lateral dynamics of the drill string in deepwater drilling. This study reviewed previous studies to determine the conditions for backward whirls, conducted numerical and small-scale model experiments, and investigated the effect of ocean currents. Consequently, the pipe clearance and friction had a significant effect, and by reflecting this in the small-scale model experimental conditions, a backward whirl was reproduced. Then, a coupling between the backward whirl and bending due to the Magnus effect was observed by towing the experimental device. Next, the results of numerical simulations and small-scale model experiments were compared, and some agreement was observed. In addition, numerical simulations showed coupled phenomena, such as an increase in the radius of the backward whirl due to the Magnus effect. Finally, the lateral dynamics of riserless drilling at a water depth of 7000 m were examined using numerical simulation. As a result, under this study’s calculation conditions, the influence of lateral dynamics was small in deepwater drilling at 7000 m. This study will contribute to understanding the dynamics of the drill string in riserless drilling.